SIR ALEX FERGUSON last night hailed Real Madrid goal hero Cristiano Ronaldo and admitted he fears his former star could come back to haunt him again in the second leg at Old Trafford.

Danny Welbeck’s first-half header ensured Man United left the Bernabeu with a precious away goal.

But Ronaldo also left his mark on the last-16 tie with a brilliant header, which he refused to celebrate in recognition of his six years at United.

And after greeting the player at the final whistle, Fergie was full of praise for the striker.

He said: “What a header. You can’t stop that. The spring, the way he holds himself in the air, the power in the header. Unbelievable. I think it was difficult for Cristiano playing against his old team as there’s a little bit of emotion for him.

“But when he gets the ball you’re praying, more than anything.”

Ferguson knows Ronaldo and Madrid pose a massive threat when the sides meet again on March 5.

He said: “Real won possession without question, but it takes us back to Old Trafford with a great chance. It will be an open game and I think we’ll score. But they are a great counter-attacking side and we have a big job on our hands.”

There was certainly enough in Real’s performance to suggest United would be unwise to claim they now hold a decisive advantage, even if Robin van Persie wasted a golden chance to seal victory on the night.

Real flew out the traps and were tearing United to shreds in the opening exchanges. Angel Di Maria went close when he cut inside and flashed a shot wide before David De Gea brilliantly denied Fabio Coentrao with a fingertip save to push the full-back’s effort onto the post.

How simple it was, too, as Welbeck shrugged off Sergio Ramos’ attentions, them climbed to head home Wayne Rooney’s corner from six yards.